DESCRIPTION: This application will continue to examine the molecular basis for the virulence of spirochetes. Utilizing Treponema denticola mutants constructed in the previous grant period, the respective roles of motility, chemotaxis, and protease activity in the formation of biofilms will be investigated. In addition, a RNA differential display approach will be used to identify genes, which are involved in colonization of solid surfaces, preformed biofilms of Porphyromonas gingivalis and Fusobacterium nucleatum, and host cell surfaces. These approaches will help to define the mechanisms, which oral spirochetes utilize in colonizing the subgingival margin. Furthermore, since penetration of tissue barriers by spirochetes appears to be an important virulence factor of these organisms, the molecular basis for this property will be examined in T denticola. Using the HUVEC transcytosis system, genes of the spirochete, which are involved in tissue penetration, will be identified using genetic approaches. It will then be of interest to determine if the syphilitic organism T pallidum utilizes a homologous set of genes to invade tissue. In addition, if the later organism utilizes species-specific invasion genes, the hypothesis that oral spirochetes, which are related to T. pallidum, may play a role in periodontitis will be examined. These approaches should increase understanding of the molecular basis for the pathogenicity of spirochetes.